System and method for automatically controlling a vehicle speed to a desired cruising speed

Abstract

A system and method for automatically controlling a vehicle speed to a desired cruising speed are disclosed in which such a control is inhibited that the opening angle is adjusted toward a prohibiting range in which an engine output torque becomes substantially constant even if the opening angle of the throttle valve is increased more than necessary. At this time, the opening angle is adjusted to a predetermined limit angle (for example, 40 degrees) and a transmission gear position is controlled depending on a difference between an instantaneous vehicle speed and a target vehicle speed. Therefore, unnecessary opening of the throttle valve exceeding the predetermined limit beyond which little increase in the engine output torque occurs can be avoided. In addition, the throttle valve can immediately be controlled from the predetermined limit to a target opening angle at which the vehicle speed can be maintained at the target vehicle speed.

What is claimed is: 
     
       1. A system for automatically controlling a vehicle speed to a desired cruising speed, comprising: (a) first means for detecting an instantaneous vehicle speed;   (b) second means for setting a target vehicle speed at which the vehicle cruises based on said detected instantaneous vehicle speed;   (c) third means for adjusting a variable of the engine output controlling mechanism of a vehicular engine so that the instantaneous vehicle speed coincides with the target vehicle speed the variable having a characteristic such that an engine output torque becomes substantially constant when the variable exceeds a predetermined limit; and   (d) fourth means for inhibiting the automatic vehicle speed control when the adjusted variable falls in a range in which the engine output torque becomes substantially constant.   
     
     
       2. A system as set forth in claim 1, wherein the engine output controlling mechanism is a throttle valve installed in an intake air passage of the engine and the variable is an opening angle of the throttle valve. 
     
     
       3. A system as set forth in claim 2, wherein the predetermined limit is substantially 40 degrees with respect to a fully closed position of the throttle valve. 
     
     
       4. A system for automatically controlling a vehicle speed to a desired cruising speed, comprising: (a) first means for detecting an instantaneous vehicle speed;   (b) second means for setting a target vehicle speed at which the vehicle cruises based on said detected instantaneous vehicle speed;   (c) third means for adjusting a variable of the engine output controlling mechanism of a vehicular engine so that the instantaneous vehicle speed coincides with the target vehicle speed, the variable having a characteristic such that an engine output torque becomes substantially constant when the variable exceeds a predetermined limit, said third means comprising: fifth means for deriving an integral error ε I  between the instantaneous vehicle speed and target vehicle speed;   sixth means for deriving a proportional error ε p  between the instantaneous vehicle speed and vehicle speed before one control period;   seventh means for deriving the adjusted variable φη on the basis of the integral and proportional errors;   eighth means for detecting an instantaneous variable of the engine output controlling mechanism;   ninth means for deriving a target variable of the engine output controlling mechanism from the adjusted variable φη derived by the seventh means and the instantaneous variable η detected by the eighth means; and   tenth means for activating the engine output controlling mechanism so as to adjust the instantaneous variable to the target variable derived by the ninth means; and     (d) fourth means for inhibiting the automatic vehicle speed control when the adjusted variable falls in a range in which the engine output torque becomes substantially constant.   
     
     
       5. A system as set forth in claim 4, wherein the fourth means comprises: (a) eleventh means for determining whether the target variable exceeds a predetermined value; and (b) twelfth means for limiting the target variable to the predetermined valve when the target variable exceeds the predetermined valve limit. 
     
     
       6. A system as set forth in claim 5, which further comprises: (a) thirteenth means for determining whether the integral error exceeds a predetermined integral error; (b) fourteenth means for changing a gear position of a vehicular transmission depending on the result of determination by the thirteenth means. 
     
     
       7. A system as set forth in claim 6, wherein the fourteenth means changes the gear position to a third gear when the integral error is less than the predetermined integral error and to an overdrive when the integral error is greater than or equal to the predetermined integral error. 
     
     
       8. A system as set forth in claim 7, wherein the vehicular transmission is an automatic transmission with the overdrive mechanism. 
     
     
       9. A system for automatically controlling a vehicle speed to a desired cruising speed, comprising: (a) first means for detecting a vehicle speed;   (b) second means for setting a target vehicle speed at which the vehicle cruises;   (c) third means for adjusting an opening angle of an engine throttle valve so that the vehicle speed coincides with the target vehicle speed, the opening angle of the throttle valve having a characteristic such that an engine output torque becomes substantially constant when the opening angle of the throttle valve exceeds a predetermined opening angle; and   (d) fourth means for inhibiting the automatic vehicle speed control when the adjusted opening angle falls in a range in which the engine output torque becomes substantially constant.   
     
     
       10. A method for automatically controlling a vehicle speed to a desired cruising speed, comprising the steps of: (a) detecting an instantaneous vehicle speed;   (b) setting a target vehicle speed at which the vehicle cruises based upon said instantaneous vehicle speed;   (c) adjusting an opening angle of an engine throttle valve of a vehicular engine so that the instantaneous vehicle speed coincides with the target vehicle speed, the opening angle having a characteristic such that an engine output torque becomes substantially constant when the opening angle exceeds a predetermined limit opening angle; and   (d) inhibiting the automatic vehicle speed control when the adjusted opening angle falls in a range in which the engine output torque becomes substantially constant.   
     
     
       11. A system for automatically controlling a vehicle speed to a desired cruising speed, comprising: (a) first means for detecting an instantaneous vehicle speed;   (b) second means for setting a target vehicle speed at which the vehicle cruises based on said detected instantaneous vehicle speed;   (c) third means for adjusting calculating a target opening variable of an engine output controlling mechanism on the basis of said detected instantaneous vehicle speed and said target vehicle speed and for adjusting an instantaneous operating variable of an engine output controlling mechanism so that said instantaneous operating variable coincides with said target operating variable and said detected instantaneous vehicle speed coincides with said target vehicle speed, said instantaneous operating variable having a characteristic such that an engine output torque becomes substantially constant when said instantaneous operating variable a predetermined limit; and   (d) fourth means for determining whether said target operating variable exceeds a predetermined limit and for limiting said target operating variable to said predetermined limit when said target operating variable exceeds said predetermined limit.